Acoustics

AET Performance to Date
We have been involved in the analysis of acoustic data from ten different pipelines. In eight cases, the testing has confirmed that the PCCP is in good shape. In these instances, the results have proven useful to the pipe owners even though no bad pipe has been detected. For example, one pipe owner was faced with a decision as to the advisability of replacing a 20-year-old, 8 km (5 mile) long pipeline due to a road widening project. The pipeline in question was manufactured by now-defunct Interpace at a time when quality was a problem. AET testing showed this particular line was in good condition and not actively deteriorating. Based on the results of this testing, the line was left in place at a savings of approximately $6 million. This decision was based in large part on the confidence that pipe owner gained from spot checks using AET for which he paid less than $50k.

In two instances, our conclusion was that the pipe was in an advanced state of deterioration. Excavation for visual inspection of the pipe surface was recommended. It is worth noting that in both instances, the pipe had been tested by a visual interior inspection (with sounding) by experienced personnel. There was no indication of distress whatsoever. In both instances, the pipe had been evaluated using over-the-line potential methods, again with no indication of distress. In both instances, our recommendation was accepted and the pipe was excavated for visual inspection.

The distress in the 252-inch pipe was detected based on less than 20 hours of data. (Reclamation) Distress in the 72-inch pipe was based on 160 hours of data collected by a pair of hydrophones spaced at 590 meters (1940 feet).

Distress in PCCP Pipe

1.8 meter (72-inch) PCCP Pipe

The Future of Acoustic Testing
We feel the future is bright for PCCP pipe owners, insofar as condition assessment and rehabilitation is concerned. Five years ago at the last meeting of the PCCP Users’ Group, there was no proven technology available to give reliable condition assessment of PCCP lines. AET is available commercially now. We expect continued advances in the AET systems. Testing and research will further increase the confidence we can place in the results. As we continue to gain experience, we will become more efficient in its use. Additional technologies will also become practicable. Developments will continue in active acoustics – impact echo and ultra-sound systems. Remote field eddy current technology shows much promise. In some instances these technologies will compliment AET to give additional information. In some instances there will be systems that compete with AET.

Pipe owners by nature are conservative. In our discussions with pipe owners regarding the use of this technology, several thoughts are frequently expressed. First, they would like to see a long list of satisfied customers before signing up to try this technology. That was a tough nut to crack, getting the first commercial customer. The list may not be long now, but there is a list and it is growing, and they are well-satisfied.

A second concern is that the price seems too high and if they wait a few years it will come down. The development of this technology is not inexpensive. There has no research or development money available in the US to defray the development costs – not federal, not AWWA, not ASCE, not ACPPA, not SBIR. These costs must be recovered. It should be noted that both AWWA Research Foundation and ACPPA have undertaken studies to evaluate various technologies, and this is a step in the right direction. Clearly if all pipe owners take the position of waiting until there is a long list of customers, and until others have absorbed the costs of technology development, it will not happen. The future for AET and other technologies will be bleak. I am sure all of us involved in the development of systems aimed at pipeline condition assessment will agree on this point: We need your support, and we need the opportunity to demonstrate that AET works now for owners of PCCP.

There is a compelling analogy between what we do with AET and what a cardiologist does with the EKG – the electrocardiogram. Both entail the use of sensors placed on a pipe to measure and analyze acoustic data. Both give a condition assessment in a relatively short test period. In 1997, PTI gave this prognosis for the future of AET:

Within ten years the use of AET in the PCCP pipelines will be as commonplace as the use of the EKG in health care today.

In the decade since, we have seen this prediction come to pass, insofar as PCCP pipelines are the “patients.”

Demonstrations and refinements of this technology have developed the confidence and support of PCCP users. AET is not the only technology used in this role, but it will continue to solidify its status as a very important tool.

Additional discussion of acoustic emission testing can be found in our library section, and on the web site of the Pressure Pipe Inspection Company – who licenses this technology from Pipetech International. www.ppic.com